The toot from Boris:
@rtanglao Answering your question from FB ;) The Heroku guide on the Mastodon site is very high level and not step by step. There is a bunch of setup that needs to be done with Mailgun - DNS, MX records, Mailgun verification and Mastodon + Heroku config. Start with the "Deploy to Heroku" and go from there. Likely best done as an "install fest" with a group of us.